1. Field of the Invention
The present invention relates to a data back-up operation of an information processing apparatus, and more particularly to a data backup operation into a storage unit in an information processing apparatus.
2. Description of the Related Art
A conventional example of a data back-up system of an information processor is described in Japanese Laid Open Patent Application (JP-A-Heisei 4-311219). In the conventional example, 2 input/output (I/O) interfaces are provided for each of large capacity storage units to back up data stored in the large capacity storage unit into a back-up unit. As is known in the art, a large capacity storage unit typically refers to mass storage devices such as an array of disks or other large capacity storage devices that generally have slower access times than main memory devices and are used for storing information that is not constantly being addressed. By using one of the I/O interfaces, a normal data transfer is performed between a main memory and the large capacity storage unit, and by using the other, the data back-up is performed from the large capacity storage unit into the back-up unit.
FIG. 1 is a block diagram illustrating the structure of the data back-up system which is proposed in the above Japanese Laid Open Patent Application (JP-A-Heisei 4-311219). Referring to FIG. 1, the data back-up system is composed of a data bus 51, a control bus 52, a central processing unit (CPU) 53, a main memory 54, a main disk control mechanism 55, a back-up disk control mechanism 56, N magnetic disk units 70X (701 to 70N) each having two I/O interfaces, a back-up RAM 60 as a back-up file memory, and a back-up unit 61. In FIG. 1, 80X (X=1, 2, . . . , N) is a main I/O interface and 90X (X=1, 2, . . . , N) is a back-up I/O interface.
However, the conventional back-up system has the following problems.
That is, the first problem is in that if the content of the storage unit 70X is updated while the back-up operation is performed, there is possibility that it becomes not possible to take the coincidence between the updated content of the storage unit 70X and the backed-up content. In such a case, the back-up operation needs to be immediately stopped such that the back-up operation needs to be re-started. This is because the single storage unit 70X can be accessed through the two I/O interfaces in the above conventional back-up apparatus. Accordingly, when one storage unit is accessed so that a plurality of portions of the content of the storage unit is updated, there is possibility that a part of the content of the storage unit is updated well sum of the content is not updated.
The second problem is in that a complicated mechanism is needed for the back-up operation. This is because each of the plurality of storage units needs to have the two I/O interfaces.